Modeling species density for conservation through integrating occupancy and telemetry data
It is often highly desirable to know not only where species are likely to occur (i.e., occupancy) but also how many individuals are supported by a given habitat (i.e., density). For many animals, occupancy and density are likely determined by separate and distinct ecological processes. Here, we model expected density on a landscape as the product of a landscape-scale occupancy probability and a habitat-scale density given occupancy. One can conceptualize our modeling process as fully packing a landscape with home ranges based on habitat quality, and then subtracting home ranges based on a probabilistic process that accounts for the fact that heterogeneous landscapes are rarely at maximum density (e.g., due to elevation, latitude, etc.).
We develop and apply this model to the Black-backed Woodpecker (Picoides arcticus) in California, a species of conservation concern. Occupancy is derived from a regional monitoring effort, while density given occupancy comes from a telemetry study of home-range size variation. Both models are combined to interpolate expected density of Black-backed Woodpeckers within the 400 sq mile Rim fire which burned in 2013. The resultant model provides a critical tool for resource managers to understand trade-offs in preserving area for burned forest habitat versus managing for other post-fire goals. Our model also outlines a potential method for modeling density beyond simple occupancy for other rare and elusive species.